Categorical Imperative

The 'Categorical Imperative (CI)' is the central principle of Immanuel Kant's moral philosophy. It serves to test maxims—subjective principles of action—for their moral permissibility. The imperative functions as a process of elimination, finding absolute and at the same time universal principles. Hence, categorical.

Only those maxims that withstand a certain test may be followed. It does not show what is morally required, but what is morally not permissible. Within this framework, there emerges a broader scope for morally permitted actions, allowing for individual discretion.

Kant formulates the CI in three equivalent, complementary versions that should always lead to the same moral judgment when correctly applied:

Ground Formula (Formula of Universal Law)

Act only according to that maxim whereby you can at the same time will that it should become a universal law.

→ This version tests the logical consistency of a maxim when generalized. It asks: Can I will that everyone in the same situation act as I do?

Humanity Formula

Act in such a way that you treat humanity, both in your own person and in the person of every other, always at the same time as an end and never merely as a means.

→ This formula highlights the dignity of humans, considering them as an end in themselves. It poses the question: Do I respect the autonomy of all involved, or do I merely use others for my purposes?

Formula of Autonomy (Realm of Ends)

Act so that all maxims from your personal legislation can harmonize into a possible realm of ends as a realm of nature.

→ This version examines the coherence of all maxims in regard to a universal, autonomous existence. It questions: Could all people live autonomously and with dignity under these rules?

Overall, the 'Categorical Imperative' represents a standard of rational morality, based on autonomy, universalizability, and respect for humans as ends in themselves.

Adjustments in the Theory of Practical Reason

Those who do not see a way out in the categorical imperative might orient themselves according to the theory of practical reason →. Julian Nida-Rümelin's theory of practical reason takes up Kant's categorical imperative but fundamentally modifies it by integrating it into the concept of structural rationality.

While Kant grounds the categorical imperative as an unconditional, formal principle of morality that measures actions solely by their universalizability, Nida-Rümelin emphasizes the embedding of actions in broader practice structures, legitimized through deliberation and balancing of reasons.

A scene in the film 'Irrational Man' with Joaquin Phoenix and Emma Stone makes the difference more accessible. In a dialogue →, Kant's categorical imperative and its absolute stance on truthfulness are critically discussed. The course of the conversation reveals the following argumentation.

According to Kant, in a morally perfect world, there would be absolutely no room for lies, as even the slightest untruth would undermine the categorical imperative.

This is illustrated by two examples. Once a murderer asks for the hiding place of his hidden victim—according to Kant, one must answer truthfully. While some might still rationally find a way out of this situation as to why they still lie in this case, the second example shows the borderline case. The Nazis ask for the hidden Anne Frank and her family—here, too, Kant's strict interpretation would require one to tell the truth.

The scene in the film shows the problematic consequences of a too rigid interpretation of the categorical imperative, which is also picked up by Nida-Rümelin's later criticism. He argues for a more flexible approach that better takes complex contexts of action into account. In this way, worldviews and ideologies can be examined under the framework of Cultural Foresight →.

Core Differences from Kant's Position

Structural rationality vs. formal maxim examination

Nida-Rümelin criticizes that Kant's imperative is too rigid to capture complex contexts of action. Instead of universal maxims, he demands a rationality that evaluates actions by their integration into desirable practice forms—such as just institutions or coherent life designs.

Example: A lie might already formally fail in Kant but be permissible in Nida-Rümelin's theory if it is part of a structurally intact communication practice.

Reasons as propositional content

In contrast to Kant's autonomy of reason, Nida-Rümelin anchors practical reasons in an intersubjective justification practice5. Moral norms do not arise from mere rational self-governance but from the ability for detached reflection on shared conditions of action.

Criticism of the optimization paradigm

Nida-Rümelin rejects both Kant's deontological rigor and consequentialist calculations. Instead of